Testicular Function and Sperm Production Flashcards
what occurs in the testes? (2)
- spermatogenesis
- hormone synthesis (not just steroidogenesis)
what occurs in the scrotum and spermatic cord?
thermoregulation
describe the process of spermatogenesis (5)
- high speed manufacturing: 35-200,000; this plant must be air-conditioned
- finishing steps: fluid absorption, membrane changes, nuclear and flagellar stabilization, motility, cytoplasmic droplet translocation
- warehouse and shipping: storage or spermatozoa for ejaculation (thanks to smooth muscle contraction upon sexual stimulation)
- final alterations and packaging: metabolic substrates, surface coatings, and transport for spermatozoa
- delivery system: erection, protrusion, emission, ejaculation
what do you want spermatic cord and scrotum temperature to be relative to body temperature?
want 2-4 degrees below body temperature
describe scrotal thermoregulation and heat transfer (2)
- vaginal cavity between the vaginal tunics contains vaginal fluid for lubrication and mobility, regulates heat transfer by allowing sliding of the testes
- scrotal smooth muscle regulates heat transfer by smooth muscle contraction or relaxation (relax muscle to drop testes away from body wall to allow more heat transfer with environment to cool down)
what are 6 kinds of scrotal lesions that impair thermoregulation
- frostbite
- warts (common in younglings)
- puncture wound
- melanoma (common in grey stallions)
- brucella dermatitis
- allergic dermatitis
do all species have scrotal testes?
nope; elephants, dolphins, armadillos, hedgehogs
describe the spermatic cord (4)
- suspends the testis in the scrotum
- connects the testis with the body
- vascular, nerve, and lymphatic supply
- houses the deferent ducts
does the cremaster muscle contribute to thermoregulation?
not too much; is a striated muscle so cannot hold contraction for prolonged periods of time
how does blood flow contribute to thermoregulation?
countercurrent heat transfer; artery passes heat to veins, so artery gets cooler as enter testes
what is important to remember regarding the connection between the abdomen and the testes?
infections on either side can lead to infections in the other!
what 5 things can impair thermoregulation?
- environmental heat
- systemic fever
- local heat due to local inflammation or infection
- adhesions between the vaginal tunics
- fat in the scrotal neck or within the scrotum
describe the testicular parenchyma
2 compartments:
1. tubular compartment: contains seminiferous tubules, germ cells, and sertoli cells, with peripheral adluminal and deep adlimunal comparments
2. interstitial compartment: contains leydig cells
describe hormonal control of testicular function (6)
- males only have tonic release of GnRH (no surge center like in females)
- frequent, low pulses of LH and FSH
- LH stimulates testosterone secretion by leydig cells
- testosterone suppresses FSH release, and in the seminiferous tubules supports sertoli cells and spermatogenesis
- a small portion of the testosterone is released systemically and supports accessory sex glands and male characteristics
- FSH supports sertoli cells
what happens to the small amount of testosterone released into systemic circulation?
it is converted to dihydrotestosterone by 5alpha-reductase to support secondary male characteristics like muscle growth, strength and endurance, bone mass density, and fat distribution
what are the 4 functions of the sertoli cells?
- establish the blood-testis barrier: via tight junctions between sertoli cells to ensure that the microenvironment in the adluminal compartment is not affected by blood changes
- phagocytosis of dying germ cells
- growth factors for germ cells
- structural support for germ cells (cytoplasmic sertoli cell projections cradle sperm cells)
list and describe the 3 phases of spermatogenesis
- proliferation phase: occurs at basement membrane of seminiferous tubules, mitotic divisions of diploid spermatogonia, this process begins in waves to ensure constant sperm production; spermatogonia migrate to adluminal compartment
- in the adluminal compartment, spermatogonia differentiate into primary spermatocytes, initiating meiosis I, which results in secondary spermatocytes that initiate meiosis II, resulting in haploid spermatids
- the round spermatids enter spermiogenesis (differentiation phase) where no further cell division occur, but cells transform into spermatozoa
describe the transformations from spermatid to spermatozoa (5)
- nucleus: elongates, but still holds DNA for fertilization and embryo development
- centrioles: realign distally and become flagella for motility
- golgi: become acrosomes that secrete enzymes for oocyte penetration and fertilization
- cytoplasm: most is lost, but some is engulfed to a droplet that is lost in ejaculation
- mitochondria and plasma membrane relatively the same
describe sperm anatomy and function
head: acrosome and nucleus
midpiece: mitochondria
tail: flagellum
sperm are highly specialized self-propelling DNA-delivery devices
on average, how long does it take for spermatogonium to become a mature sperm available for ejaculation? is this affected by frequency of ejaculation? what does this mean regarding recovery of sperm production following damage?
takes 2 months on average with slight species differences, not affected by frequency of ejaculation! this means that recovery of sperm production following transient damage takes approximately 2 months
what happens at ejaculation?
- sperm are moved from epididymal tail through deferent ducts and into urethra via smooth muscle contractions
- as they move through the duct system, sperm are mixed with fluids from ducts and accessory sex glands (prostate only in dogs, vesicular, prostate, and bulbourethra in stallions)
describe seminal plasma (6)
- liquid, noncellular portion of semen
- fluid vehicle for sperm transport and delivery
- forms a gel pulg in boars and stallions
- oxytocin and PGF2alpha to induce uterine contractions
- source of energy for sperm (glucose or fructose)
- prevents sperm phagocytosis in uterus
describe the 3 ejaculatory fractions
- first/pre-sperm fraction: from prostate or bulbourethral gland, watery and cleanses urethra
- second, sperm-rich fraction: from the epididymis, ampulla, and prostate, milky and contains most spermatozoa
- third fraction: from vesicular glands or prostate, a clear gel thatw ashes out remaining sperm
